Two-Stage Linear Peristaltic Pump Mechanism

ABSTRACT

This invention discloses a peristaltic pump composed of a two-stage linear peristaltic pump mechanism, which engages in different functions, charging and pumping a fluid to a patient. This peristaltic pump is capable of restoring the crushed tubing, caused by repeated compression or crushing of the tubing by peristaltic fingers, to its original circular cross sectional area so that it can provide a precise flow rate. The two-stage linear peristaltic pump mechanism substantially improves the consistency of a flow rate over time and extends the usefulness of peristaltic pumps to applications where they could not otherwise be used.

BACKGROUND OF THE INVENTION

This invention is related to a peristaltic pump that is capable of providing a precise and substantially consistent flow rate over a substantial cumulative operating time including by maintaining or restoring crushed or deformed tubing back to its original circular cross section.

When linear peristaltic mechanisms are used as the fluid pumping device in standard tubing large volume infusion pumps, a problem in maintaining flow rate accuracy is inherent over time due to a tubing crush. The tubing crush is caused by repeated compression or crushing of the tubing by the peristaltic fingers. The crush can create a set that does not allow the tubing over time to return to its original circular cross section, but rather it becomes more and more elliptical. Since the cross sectional area of an ellipse is less than the original circle, the flow rate diminishes over time as the cross sectional area diminishes.

Some pumps use silicone or Silastic tubing which is more resilient and therefore less likely over time to suffer a diminishment in cross sectional area. However, Silastic tubing is more expensive than standard tubing as well as being proprietary in nature and not being available from multiple sources.

In other pumps compensation for the reduction in the flow rate is provided by running the motor faster over time. A predictive algorithm, typically in software, is used to determine how fast to run the motor over time. However, software algorithms to compensate are approximations at best and subject to significant error because of inevitable variations in tubing durometer that occur from production lot to lot.

Some ways to control flow rate in pumps are disclosed in U.S. Pat. No. 5,431,634, U.S. Pat. No. 7,559,926, and U.S. Pat. No.7,566,209. U.S. Pat. No. 5,431,634 used a diaphragm pump to maintain an output volume substantially constant notwithstanding substantial variation in fluid pressure from a fluid supply or variation in ambient pressure. US Pat. No. 7,559,926 details an implantable infusion drug pump that pumps a fluid into a main reservoir then out through a flow restrictor. The restrictor is able to limit the flow rate to the extent dictated by a motivating force, fluid viscosity, and restriction. US Pat. No. 7,566,209 relates to a peristaltic pump that controls the volume of the fluid in the tubing utilizing a magnetic and/or an electric field. However, none of those patents provides a mechanism capable of accurately compensating for the reduction of the flow rate due to the tubing crushing inherent in a peristaltic pump by restoring the crushed tubing to its original circular cross section.

SUMMARY

A peristaltic pump having a tubing in a fluid communication with a reservoir containing a fluid, the peristaltic pump comprises a two-stage linear peristaltic pump mechanism: one stage linear peristaltic pump mechanism ensures a crushed area of the tubing on which the other stage pump mechanism operate to return to its original cross sectional area and to provide a consistent flow rate of the fluid. These and other features, aspects, and advantages of the present invention will become better understood with reference to the following description, appended claims, and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a perspective view of the peristaltic pump assembly according to an exemplary embodiment of the present invention;

FIG. 1B is a partial sectional view of FIG. 1A;

FIG. 2A is an isolated perspective view of operation of the charging mechanism, sub-assembly of the peristaltic pump of FIG. 1A;

FIG. 2B shows a charging cycle for the charging mechanism of FIG. 2A;

FIG. 2C is similar to FIG. 2A but is a view of the pumping mechanism of the peristaltic pump;

FIG. 2D shows a pumping cycle for the pumping mechanism of FIG. 2C;

FIG. 3 is an exploded view of the peristaltic pump subassembly;

FIG. 4 is an enlarged view of a charging occluder mechanism according to an exemplary embodiment of the present invention;

FIG. 5 is a block diagram of one exemplary electronics control;

FIG. 6 shows a flowchart of the program to operate the peristaltic pump of this invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The present invention provides that a crushed area of a piece of tubing caused by repeated press of a peristaltic pump 8 is always returned to or toward its original cross sectional area with each pump cycle. Thus, this provides an equal or a substantially equal flow rate of a fluid in each cycle deterring or eliminating a flow reduction problem. In one aspect of the invention, this return to substantially original cross sectional area for the tubing is accomplished by using a two-stages linear peristaltic pump mechanism 12. Specifically, one stage linear peristaltic pump mechanism ensures a crushed area of the tubing on which the other stage pump mechanism operate to return to its original cross sectional area and to provide a consistent flow rate of the fluid.

The two-stage linear peristaltic pump mechanism 12 can be used for any pumping function including but not limited to providing a fluid to a spray nozzle as but one example. Another example is an infusion pump. Because the two-stage linear peristaltic pump mechanism 12 substantially improves flow rate consistency over time, the two-stage linear peristaltic pump mechanism 12 extends the usefulness of peristaltic pumps to applications where they could not otherwise be used.

Referring to FIGS. 1A and 1B, there is shown three dimensional and front, partial views of one embodiment of the assembly of the peristaltic pump 8 made in accordance with the present invention. A piece of tubing 16 in fluid communication with a reservoir 10 containing a fluid is used together with the peristaltic pump 8. The two-stage linear peristaltic pump mechanism 12 comprises two separately controlled, but cooperatively working, pumping stages. They are an upstream linear peristaltic charging mechanism 22 (charging mechanism 22) and a downstream linear peristaltic pumping mechanism 24 (pumping mechanism 24). The charging mechanism 22 and the pumping mechanism 24 are successively along the upstream portion of the tubing 16 a, a charging section 18 of the tubing 16, and downstream portion of the tubing 16, a pumping section 20 of the tubing 16, to infuse a fluid to a patient through the tubing 16. The charging mechanism 22, acting upon the charging section 18 of the tubing 16, pumps the fluid from the charging section 18 of the tubing 16 into the pumping section 20 of the tubing 16. The charging mechanism 22 is responsible for ensuring that the pumping section 20 of the tubing 16, which will subsequently be acted on by a pumping mechanism 24, is fully extended or is filled to an extent as specified and under pressure, countering the effects of any crushing it may have experienced, before the pumping mechanism 24 begins its work. The pumping mechanism 24, acting upon the pumping section 20 of the tubing 16, pumps the fluid from the pumping section 20 of the tubing 16 into a patient at an equal or a substantially equal flow rate.

The tubing 16 is any of a number of standard commercially available intravenous tubing with different inner diameters.

The charging mechanism 22 comprises a plurality of peristaltic charging fingers 30 a and a charging shaft 26 a; the pumping mechanism 24 comprises a plurality of peristaltic pumping fingers 30 b and a pumping shaft 26 b. In one embodiment, the charging shaft 26 a and pumping shaft 26 b are crank shafts; in another embodiment, cam shafts are used in replacement of those crank shafts. The number of peristaltic charging fingers 30 a and peristaltic pumping fingers 30 b are 5-14 or 5-8.

A motor or two motors 34 such as DC motor, step motor, or brush motor or brushless motor, not limited to the aforementioned, drives a motor shaft 40 that turns the charging shaft 26 a and the pumping shaft 26 b in a successive series. In one embodiment, each shaft of the charging shaft 26 a and the pumping shaft 26 b is independently driven by a same single motor 34 in one direction via one-way clutches 44 a and 44 b such as sprag or roller clutches, which allow a motor to drive in one direction but to disengage in the other direction.

In one embodiment, the motor 34 is a single DC gear motor. The motor 34 together with a quadrature encoder 36 and those two roller clutches 44 a and 44 b drives, via the motor shaft 40 connected with the motor 34 and, through a motor gear 42, via a main shaft 48, the charging mechanism 22 and the pumping mechanism 24 in series. Main gears 46, 46 a, and 46 b are attached on or connected with the main shaft 48. The main gear 46 drives either the main gear 46 a or 46 b in one direction and disengage in the other direction while 46 a and 46 b separately runs gears 32 a, which is in connection with the charging shaft 26 a, and 32 b, which runs the pumping shaft 26 b. The motor 34 can be any of a number of commercially available motors such as the Maxon Amax series, Maxon Motor Inc., Fall River, Mass. including an integral quadrature encoder 36, detecting the speed and direction of the motor 34, and a gear box 38, slowing down the speed of the motor 34 and at the same time increasing power output. The motor 34 is attached to a base 50 or an equivalent structure for steadfastness.

In one embodiment, the motor 34 is a single DC gear motor together with a quadrature encoder 36 and the two roller clutches 44 a and 44 b driving, via the motor shaft 40 connected with the motor 34, the charging mechanism 22 and the pumping mechanism 24 in series. The main gears 46, 46 a, and 46 b are attached on or connected with the motor shaft 40. The main gear 46 drives, either the main gear 46 a or 46 b, in one direction and disengage in the other direction while main gears 46 a and 46 b separately run the gear 32 a, which is in connection with the charging shaft 26 a, and the gear 32 b, which is in connection with the pumping shaft 26 b.

The quadrature encoder 36 is used to control the speed and direction of the motor 34. When the motor 34 turns in one direction, one of those two one-way clutches 44 a mating the main gear 46 a and 44 b mating the main gear 46 b via either the gear 32 a or 32 b, or directly engages turning one of two shafts, the charging shaft 26 a and the pumping shaft 26 b.

Referring to FIGS. 2A, 2B, 2C, and 2D, the charging mechanism 22 is designed so that, when the motor 34 is driving in the clockwise direction, the charging mechanism 22 is driven by the roller clutch 44 a and the peristaltic charging fingers 30 a produce a downstream peristaltic wave. The pumping mechanism 24 is designed so that, when the motor 34 is running in the counterclockwise direction, the pumping mechanism 24 is driven by the roller clutch 44 b and the plurality of peristaltic pumping fingers 30 b produce a downstream peristaltic wave. Thus, the running direction of the motor 34 controls which mechanism is providing the downstream peristaltic wave, and each of the charging mechanism 22 and the pumping mechanism 24 operates independent of the other; in other words the speed and rotation direction of each mechanism is separately controlled, but those two mechanism work cooperatively.

The plurality of peristaltic charging fingers 30 a, sized around the charging shaft 26 a, and the plurality of peristaltic pumping fingers 30 b, sized around the pumping shaft 26 b, when the charging shaft 26 a and the pumping shaft 26 b are turning, either compress the tubing 16 against a surface of a back member 74 or release the tubing 16.

In one embodiment, the peristaltic pump 8 further comprises a charging occluder mechanism 62 a positioned at the downstream of the charging section 18 of the tubing 16 and a pumping occluder mechanism 62 b positioned at the downstream of the pumping section 20 of the tubing 16. In one embodiment, the charging occluder mechanism 62 a comprises at least one finger of the plurality of peristaltic charging fingers 30 a adjacent to the pumping section 20 of the tubing 16. The charging occluder mechanism 62 a is able to compress the tubing 16 shut against the backing member 74 and to prevent backflow, when the pumping mechanism 24 is in operation. The pumping occluder mechanism 62 b comprises at least one selected from the group consisting of at least one finger of the plurality of pumping fingers 30 b and/or an occluder finger 58, at the downstream of the pumping section 20 of the tubing 16. The pumping occluder mechanism 62 b is able to press the tubing 16 shut against the backing member 74 for the prevention of leakage, when the charging mechanism 22 is in operation.

Referring to FIGS. 2A, 2B, 2C, and 2D, in operation, pumping the fluid to the patient is accomplished by the action of the charging mechanism 22 and the pumping mechanism 24 in successive sequence. Referring to FIGS. 2A and 2B, at the conclusion of one peristaltic cycle, the pumping occluder mechanism 62 b presses the tubing 16 shut against the backing member 74 to prevent leakage, and then, the motor 34 turns in a clockwise direction so that the charging mechanism 22 pushes the fluid from the charging section 18 of the tubing 16 toward the pumping section 20 of the tubing 16, eventually filling the pumping section 20 of the tubing 16 with the fluid. The motor 34 continues to turn and the filling of the pumping section 20 of the tubing 16 continues until a transducer 54 indicates that the pressure in the pumping section 20 of the tubing 16 has reached a level that the pumping section 20 of the tubing 16 has been fully filled with the fluid and is fully extended to restore deformed pumping section 20 of the tubing 16 to original or substantially original cross sectional area, or has been filled to an extent as specified. Then, referring to FIGS. 2C and 2D, the motor 34 stops turning clockwise and starts driving in a counterclockwise direction. The charging mechanism 22 now doesn't turn, thus remains in its final position and the charging occluder mechanism 62 a compresses the tubing 16 shut against the backing member 74 to prevent backflow. The pumping mechanism 24 is operating on the now filled pumping section 20 of the tubing 16 and pumps the fluid that was filling the pump section 20 of the tubing 16 toward the patient.

The transducer 54 is positioned in contact with an outer wall of the tubing 16 just on or beyond the pumping section 20 of the tubing 16 to measure a pressure of the outer wall of the pumping section 20 of the tubing 16. One embodiment of the transducer 54 is a force sensing resister. Another embodiment of the transducer 54 is a piezoelectric sensor.

In one embodiment, the peristaltic pump 8 is designed such that the charging mechanism 22 fills the pumping section 20 of the tubing 16 in about 30 seconds or less or a duration prescribed by an administration of a medication to have more continuous flow. To realize such a quick filling, in one embodiment, the pumping section 20 of the tubing 16 is sufficient short, and/or the motor 34 turns the charging shaft 26 a sufficient fast, and/or a total surface of the plurality of peristaltic charging finger 30 a, which is in contact with the charging section 18 of the tubing 16, is larger than that of the plurality of peristaltic pumping finger 30 b.

Referring to FIG. 3, each shaft, the charging shaft 26 a and the pumping shaft 26 b, supported by end caps 52 a, b and c and attached to a support element such as a pump train mount 56 or an equivalent for the purpose of steadfastness.

Holding elements such as clamps 68 a and 68 b or their equivalents hold the tubing 16 in place.

In one embodiment, the peristaltic pump 8 has a buffer mechanism 71 limiting potential damage forces and providing adjustment compliance when the occluder finger 58 compresses the tubing 16 shut. One embodiment of the buffer mechanism 71 comprises an occluder backer 72 together with a springs 78 held in a spring cap 76 by a set screw 80. The occluder backer 72, which is retained in position by a foot retainer 70, is made of a resilient material such as plastics. The occluder backer 72 and the spring 78 are positioned over the occluder finger 58.

In one embodiment, referring to FIG. 4, a pin 60 connected with a bias element 64, a spring or an equivalent, is affixed on the occluder finger 58, which is sized around the pumping shaft 26 b and is run by the pumping shaft 26 b. The bias element 64 is further connected with a pin 66 affixed on the pump train mount 56. Referring to FIGS. 2A, 2B, 2C, and 2D, during the time the charging mechanism 22 is operating, the occluder finger 58 compresses close the downstream of the pumping section 20 of the tubing 16; during the time the pumping mechanism 24 is operating and is moving the fluid to the patient, the spring 64 rhythmically pulls the occluder finger 58 away from the downstream of the pumping section 20 of the tubing 16 with the rotation of the pumping shaft 26 b.

FIG. 5 shows one example of an electronics control for operating the peristaltic pump 8. An electronics circuit board 90 comprises a main processor 86 and a motor processor 84. Rotary positions 82 of the charging mechanism 22 and the pumping mechanism 24 relative to the rotary position of the motor shaft 40 are prestored in the motor processor 84. The transducer 54 measuring the pressure of the outer wall of the pumping section 20 of the tubing 16 feeds pressure data to the motor processor 84; the motor processor 84 monitors the speed and direction of the motor 34 by the encoder 36. At that point when the transducer 54 indicates that the pumping section 20 of the tubing 16 has been fully filled with the fluid or has been filled to an extent as specified, the motor 34 controlled by the encoder 36 stops turning clockwise and starts driving in a counterclockwise direction after taking into consideration the rotary positions 82. In contrast, at the point when the pumping section 20 of the tubing 16 is empty or substantially empty, the motor 34 controlled by the encoder 36 stops turning counterclockwise and starts driving in a clockwise direction after taking into consideration the rotary positions 82. In one embodiment, the emptiness and substantial emptiness is indicated by the transducer 54. Alarm 88 is connected to the main processor 86 and the alarm 88 is activated by the main processor 86 to warn when any specified operative faults occur. A display 92, keypad 94, and electric power 96 are connected to the main processor 86.

In one embodiment, the two-stage linear peristaltic pump mechanism 12 further comprises a two-stage pumping mechanism program which operates the peristaltic pump 8; FIG. 6 illustrates how the two-stage pumping mechanism program operates the peristaltic pump 8. In Step 100, to start the operation of the peristaltic pump 8, the motor 34 runs to drive the pumping mechanism 24 so that a pumping occluder mechanism 62 b closes the downstream of the pumping section 20 of the tubing 16. In Step 102, the motor 34 runs to drive the charging mechanism 22 and fill the pumping section 20 of the tubing 16 while the motor 34 disengages the pumping mechanism 24. In Step 104, a determination is made as to whether the transducer 54's pressure is greater than or equal to a predetermined value indicating that the pumping section 20 of the tubing 16 has been fully extended or it has been filled to an extent as specified. If “no” in Step 104, go to Step 102; if “yes,” go to Step 106. In Step 106, the motor 34 continues running to drive the charging mechanism 22 so that the charging occluder mechanism 62 a presses the charging section 18 of the tubing 16 shut to prevent backflow. In Step 108, the motor 34 runs to drive the pumping mechanism 24 and to move the fluid further along while the motor 34 disengages the charging mechanism 22. In Step 114, a determination is made as to whether the pumping mechanism 24 has finished a requested pumping task. If “yes,” go to Step 100; if “no,” go to Step 108. In Step 110, an inquire is made as to whether the transducer 54 is measuring a pressure greater than or equal to a predetermined threshold occlusion value such as 15 psi indicating that an occlusion may exist. If “yes” is an answer to this inquiry, the alarm 88 warns and the motor 34 stops. In one embodiment, the requested pumping task is defined to empty or substantially empty the pumping section 20 of the tubing 16.

The above examples are illustrative only. Variations obvious to those skilled in the art are a part of the invention. Additionally, the present invention does not require that all of the advantageous features and all of the advantages stated need be incorporated into every embodiment. 

What is claimed is:
 1. A peristaltic pump configured to act on a piece of tubing in fluid communication with a reservoir containing a fluid, the peristaltic pump comprising a two-stage linear peristaltic pump mechanism, wherein one stage of the two-stage linear peristaltic pump mechanism ensures a crushed area of the tubing on which the other stage of the two-stage linear peristaltic pump mechanism operates is returned to an original cross sectional area and to provide a consistent flow rate of the fluid through said piece of tubing.
 2. A peristaltic pump as recited in claim 1, wherein the two-stages of the linear peristaltic pump mechanism comprise a charging mechanism configured to be positioned along an upstream charging section of the piece of tubing and a pumping mechanism configured to be positioned along a downstream pumping section of the piece of tubing, the charging mechanism and pumping mechanism cooperating such that when the pumping mechanism is not operating, the charging mechanism operates on the charging section of the tubing to fill the pumping section of the tubing with the fluid, and such that when said charging mechanism is not operating, the pumping mechanism operates on the pumping section of the tubing to moves said fluid further along.
 3. A peristaltic pump as recited in claim 2, wherein the charging mechanism comprises a charging shaft and a plurality of peristaltic charging fingers sized around the charging shaft, wherein the pumping mechanism comprises a pumping shaft and a plurality of peristaltic pumping fingers sized around the pumping shaft.
 4. A peristaltic pump as recited in claim 3, further comprising a backing member cooperating with the charging mechanism and the pumping mechanism such that when the charging mechanism is operating, the charging shaft turns the plurality of peristaltic charging fingers to compress the charging section of the tubing against the backing member, and when the pumping mechanism is operating, the pumping shaft turns the plurality of peristaltic pumping fingers to compress the pumping section of the tubing against the backing member.
 5. A peristaltic pump as recited in claim 4, further comprising a charging occluder mechanism positioned to act downstream of the charging section of the tubing.
 6. A peristaltic pump as recited in claim 5, wherein the charging occluder mechanism comprises at least one finger of the plurality of peristaltic charging fingers downstream of the charging section of the tubing.
 7. A peristaltic pump as recited in claim 4, further comprising a pumping occluder mechanism positioned to act downstream of the pumping section of the tubing.
 8. A peristaltic pump as recited in claim 7, wherein the pumping occluder mechanism comprises at least one finger of the plurality of pumping fingers, or an occluder finger downstream of the pumping section of the tubing.
 9. A peristaltic pump as recited in claim 8, wherein the occluder finger, fitting around the pumping shaft, is connected with a bias element with an end fixed onto the peristaltic pump, wherein the occluder finger is pulled away from the tubing by the bias element when the pumping mechanism is in operation.
 10. A peristaltic pump as recited in claim 3, wherein the pumping shaft is a crank shaft or a cam shaft, wherein the charging shaft is a crank shaft or a cam shaft.
 11. A peristaltic pump as recited in claim 2, further comprising at least one driver, wherein said at least one driver is connected to turn at least one from the group consisting of said charging mechanism and said pumping mechanism.
 12. A peristaltic pump as recited in claim 11, wherein the at least one driver is at least one motor.
 13. A peristaltic pump as recited in claim 12, wherein a single motor is connected to turn both the charging mechanism and the pumping mechanism.
 14. A peristaltic pump as recited in claim 13, further comprising at least two clutches, wherein the at least two clutches are connected to said motor turning said charging mechanism to operate on said charging section of the tubing when said motor rotates in a first direction while disengaging said pumping mechanism, and turning said pumping mechanism to operate on said pumping section of the tubing when said motor rotates in a second direction while disengaging said charging mechanism.
 15. A peristaltic pump as recited in claim 14, wherein said at least two clutches are roller clutches.
 16. A peristaltic pump as recited in claim 15, further comprising a first roller clutch and a second roller clutch, wherein said first roller clutch is connected for turning said charging mechanism, wherein said second roller clutch is connected for turning said pumping mechanism.
 17. A peristaltic pump as recited in claim 16, comprising at least one first gear coupled with the first roller clutch in connection with and turning said charging mechanism, and at least one second gear coupled with the second roller clutch in connection with and turning said pumping mechanism.
 18. A peristaltic pump as recited in claim 2, wherein the charging mechanism and the pumping mechanism are operated in a successive series.
 19. A peristaltic pump as recited in claim 14, further comprising an encoder controlling the turning speed and direction of the motor.
 20. A peristaltic pump as recited in claim 19, further comprising a transducer configured and positioned on said pump to be in contact with an outer wall of the pumping section of the tubing, the transducer configured to indicate when the pumping section of the tubing has been fully filled and is fully extended, or has been filled to an extent as specified with the fluid, said transducer cooperating with the motor and charging mechanism to cease charging mechanism operation and start the pumping mechanism in response to such indication. 